动能能

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This military jet, like all jets, requires a large amount of work to get into the air; unlike most jets, this one is taking off from the deck of aircraft carrier. This requires careful coordination of the plane's engines and the ship's catapults and harnesses to accelerate the jet to about 270 km per hour in just two seconds. This incredible feat requires huge conversions.  
::这种军用喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气气气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气式喷气

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Kinetic Energy
::动能能

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Energy  is the capacity of an object to do work, and like work, energy's unit is the joule (J). Energy exists in many different forms, but the one we think of most often when we think of energy is kinetic energy . Kinetic energy is often thought of as the energy of motion because it is used to describe objects that are moving. Remember, though, that energy is the ability of an object to do work. Any moving object has the capacity to cause another object to move if they collide. This ability is what we mean when we refer to an object's kinetic energy: the ability to change another object's motion or position simply by colliding with it. The equation of an object's kinetic energy depends on its mass and :
::能量是物体的工作能力, 和工作一样, 能量的单位是焦耳。 能源以多种不同的形式存在, 但是当我们想到能源时, 我们经常想到的是动能。 动能通常被看作运动的能量, 因为它用来描述移动中的物体。 但是, 记住, 能量是物体的工作能力。 任何移动的物体如果相撞, 都有能力使另一个物体移动。 当我们提到物体的动能时, 这种能力就是我们所说的: 改变另一个物体运动或位置的能力, 只需与它相撞即可。 物体动能的方程式取决于物体的质量, 并且:

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$\begin{array}{r}KE=\frac{1}{2}m{v}^2\end{array}$
::KE=12 mv2

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The kinetic energy of a moving object is directly proportional to its mass and directly proportional to the square of its velocity. This means that an object with twice the mass and equal will have twice the kinetic energy while an object with equal mass and twice the speed will have quadruple the kinetic energy.
::移动对象的动能与其质量直接成正比,与其速度的平方直接成正比。这意味着,质量和速度相等两倍的物体将拥有两倍的动能,而质量和速度相等的物体将拥有三倍的动能。

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The kinetic energy of an object can be changed by doing work on the object. The work done on an object equals the kinetic energy gain or loss by the object. This relationship is expressed in the work-energy theorem $\begin{array}{r}{W}_{\text{NET}}=\mathrm{\Delta }KE\end{array}$ .
::物体的动能可以通过对物体进行工作来改变。在物体上完成的工作等于物体的动能增益或损耗。这种关系表现在工作能量理论WNETQQKE中。

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Examples
::实例

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Example 1
::例1

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A farmer heaves a 7.56 kg bale of hay with a final velocity of 4.75 m/s.
::农民堆积7.56公斤干草,最后速度为4.75米/秒。

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(a) What is the kinetic energy of the bale?
:a) 白藻的动能是什么?

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(b) The bale was originally at rest. How much work was done on the bale to give it this kinetic energy?
:b) 白鲸最初处于休息状态,在白鲸上做了多少工作,以提供这种动能?

 

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(a) $\begin{array}{r}KE=\frac{1}{2}m{v}^2=\left(\frac{1}{2}\right)(7.56\text{kg})(4.75{)}^2=85.3\text{Joules}\end{array}$
:a) KE=12 mv2=(12)(7.56公斤)(4.752)=85.3焦耳

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(b) $\begin{array}{r}\text{Work done}=\mathrm{\Delta }KE=85.3\text{Joules}\end{array}$
:b) 已完成的工作____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Example 2  
::例2

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What is the kinetic energy of a 750. kg car moving at 50.0 km/h?
::以50公里/小时的速度行驶的750公斤汽车的动能是多少?

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  $\begin{array}{r}\left(\frac{50.0\text{km}}{\text{h}}\right)\left(\frac{1000\text{m}}{\text{km}}\right)\left(\frac{1\text{h}}{3600\text{s}}\right)=13.9\text{m/s}\end{array}$

:5 000公里)(1000公里)(1 h3600秒)=13.9米/秒)

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$\begin{array}{r}KE=\frac{1}{2}m{v}^2=\left(\frac{1}{2}\right)(750.\text{kg})(13.9\text{m/s}{)}^2=72,300\text{Joules}\end{array}$
::KE=12 mv2=(12)(750公斤)(13.9 m/s)2=72 300 焦耳

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Example 3  
::例3

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How much work must be done on a 750. kg car to slow it from 100. km/h to 50.0 km/h?
::要将一辆750公斤的汽车从100公里/小时拖慢到50.0公里/小时,还需要做多少工作?

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From the previous example problem, we know that the  $\begin{array}{r}KE\end{array}$ of this car when it is moving at 50.0 km/h is 72,300 Joules.  If the same car is going twice as fast, its  $\begin{array}{r}KE\end{array}$ will be four times as great because  $\begin{array}{r}KE\end{array}$ is proportional to the square of the velocity.  Therefore, when this same car is moving at 100. km/h, its  $\begin{array}{r}KE\end{array}$ is 289,200 Joules.  Therefore, the work done to slow the car from 100. km/h to 50.0 km/h is $\begin{array}{r}(289,200\text{Joules})-(72,300\text{Joules})=217,000\text{Joules}\end{array}$ .
::从上一个例子问题中,我们知道该车在50公里/小时移动时的KE是72 300 Joules,如果同一车的行驶速度是其速度的两倍,那么其KE将是其速度平方的四倍,因为KE与速度的平方成正比。因此,当该车的行驶速度是100公里/小时,其KE是289 200 Joules。因此,将车速从100公里/小时减慢到50公里/小时的工程是(289 200 Joules)-(72 300 Joules)=217 000 Joules。

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Kinetic energy is an important concept when we think about how fast a proton must travel through a particle accelerator in order to smash apart the nucleus of another atom. Observe the graph in the following simulation that illustrates the kinetic energy of a proton as a function of speed. The shape of this graph is parabolic (quadratic) because the kinetic energy of the proton depends on the square of the speed   ( $\begin{array}{r}KE=\frac{1}{2}{mv}^2\end{array}$ )  . To double the speed, you need four times as much energy. To triple the speed, you need nine times as much energy. See if you can adjust the sliders to generate the enormous amount of kinetic energy needed to smash the atom:
::当我们思考质子在粒子加速器中飞行速度必须有多快才能粉碎另一个原子的核时,动能是一个重要的概念。 在以下模拟中观察显示质子动能的图形, 以速度函数来显示。 这个图的形状是parabolic( 夸度) , 因为质子的动能取决于速度的正方形( KE=12mv2) 。 要将速度增加一倍, 您需要四倍的能量。 要将速度提高三倍, 您需要九倍的能量。 看能否调整滑动器以产生击碎原子所需的大量动能 :

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Further Reading
::继续阅读

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Summary
::摘要

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• Energy is the ability to change an object’s motion or position.
  ::能量是改变物体运动或位置的能力。
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• The energy of motion is called kinetic energy.
  ::运动的能量叫动能能量
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• The formula for kinetic energy is $\begin{array}{r}KE=\frac{1}{2}m{v}^2\end{array}$ .
  ::动能公式为 KE=12 mv2。
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• The work done on an object equals the kinetic energy gain or loss by the object, $\begin{array}{r}{W}_{\text{NET}}=\mathrm{\Delta }KE\end{array}$ .
  ::在物体上完成的工作等于物体WNETQKE的动能增益或损耗。

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Review
::回顾

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1. A comet with a mass of $\begin{array}{r}7.85\times {10}^{11}\text{kg}\end{array}$  is moving with a velocity of 25,000 m/s. Calculate its kinetic energy.
   ::质量为7.85×1011公斤的彗星正以25 000米/秒的速度移动。计算其动能。
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2. A rifle can shoot a 4.00 g bullet at a speed of 998 m/s.
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   1. Find the kinetic energy of the bullet.
      ::找到子弹的动能
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   2. What work is done on the bullet if it starts from rest?
      ::如果子弹从休息开始,会做什么工作?
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   3. If the work is done over a distance of 0.75 m, what is the average force on the bullet?
      ::如果工作在0.75米的距离内完成,子弹的平均强度是多少?
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   4. If the bullet comes to rest after penetrating 1.50 cm into a piece of metal, what is the magnitude of the force bringing it to rest?
      ::如果子弹在穿透1.50厘米的金属碎片后 进入休息状态 子弹的强度是多少?
   
   ::步枪可以以998米/ 秒的速度射出4. 00克的子弹。 找到子弹的动能。 如果子弹从休息开始, 弹体会做哪些工作? 如果工作在0. 75米的距离内完成, 子弹的平均力是多少? 如果子弹穿透1. 50厘米的金属碎片后, 弹体会休息, 其强度会如何?

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Explore More
::探索更多

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Use this resource to answer the questions that follow.
::使用此资源回答下面的问题 。

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1. Potential energy is present in objects that are ______________.
   ::具有潜在能量的物体为_______。
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2. Kinetic energy is present in objects that are ______________.
   ::动能存在于的物体中。
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3. What formula is given for kinetic energy?
   ::动能的公式是什么?